This invention relates to paint spray booths and paint or sludge recovery systems and method for such booth, and more particularly, to water washed booths that utilize one or more weirs and a solids separator.
Heretofore, water washed paint spray booths have utilized sludge recovery systems to separate the spent paint material picked up by the water as it passed through the booth. In one type system, the water carrying the spent paint is allowed to drop or flow out of the booth into a recovery tank or pit. In the tank or pit, the water is treated with chemicals, such as flotation chemicals which assists the spent paint material to separate or segregate, and, in this instance, float to the top. After sufficient time for the separating or flotation action to occur, the spent paint material floats to the top and is allowed to flow over a weir into a separation area wherein it can be concentrated. From there, the concentration spent paint material is drawn off to a centrifuge which separates the spent paint from the remaining water, and the remaining water is sent back and is reused in booth.
During the operation of the booth, and even during downtime, water in the booth system tends to be reduced in quantity, either due to evaporation, water being blown out the booth eliminator section (the booth having a motor driven fan to usually exhaust air, including some water out of the booth) and just variations in operating conditions. The latter could be due to a single pit or tank serving more than one booth and one or more booths operating conditions being changed or shut down. Changes in both water quantity and consequently the water level and the sludge recovery can have adverse consequences, particularly on the operations of sludge systems using weirs. For example, changes of water level effects the water crests flowing over the weirs and their operation. Too large a water crest can cause excess water to be supplied to the separator making it more difficult to extract the sludge efficiently. Too little water in the crests, on the other hand, can cause hang ups of the sludge, and partial or complete blockages, and also reduces the efficiency of the operation. Keeping a constant water level in the tank is important as it helps keep weirs operating consistently. Heretofore, one attempt to do so was to try to use a float controlling the make up water valve in the large pit in which the chemical action or flotation action takes place. While this system worked, it was slow to react to changes and allowed considerable variation in water level in other portions of the system. Due to the difficulty in controlling the water level in such way, it was difficult to get consistent efficient operation of a system based on paint sludge flotation and some times other systems were used such as sinking or suspension, that is, causing the spent paint to first sink, be drawn off the bottom or to be kept in suspension and just drawn off. Prior to the present invention, there was not a reliable way to maintain water level efficiently and permit the use of spent paint flotation and weirs.
The present invention provides structure or means and a method to better maintain the water level in a paint spray booth sludge recovery system to make the use of flotation and weirs highly efficient.
In the improved system, the water level is not measured in the large tank or pit of the chemicals section, but is instead measured downstream, preferably, in a weir box having an entrance weir into which the water flows after the spent paint is treated and concentrated and/or separated by flowing over this entrance weir. The invention provides excellent control of the water level in the tank and a rapid response to a change in water may provide make up water. In the present invention, water and dispersed spent paint is taken out from the weir box to flow to the solids separation device, in this instance, a centrifuge where the sludge is essentially separated from the water. The sludge-free water is first passed through screens and sent back to the booth pumps that provide the water circulation (recirculation) for the booth for reuse.
Another improvement is the provision of an agitation system within the weir box to keep the water and any spent paint material agitated so that the spent paint does not settle out. This agitation water flow from the weir box may be provided by a pump that returns water to the weir box to keep it agitated.
Another improvement is the provision of a sludge withdrawal system which may utilize a separate pump to pick up water and sludge at the bottom of a drop tank into which the booth first discharges the water and spent paint, before the first weir. The material from the sludge withdrawal system is then discharged into a basket or screened area in the pit or tank to trap large sized spent paint material or sludge, but let the water escape. If desired, the drop tank too may be provided with means for agitating the spent paint and water therein.
Additionally, a maintenance cycle may be provided with means for withdrawing water and solids from any desired portion of the booth or tank and returning cleaned water to the system. Preferably, this action occurs in the tank before the first weir or drop section to keep it clean.
The entire operation of the booth tank and sludge removal system may be automatically controlled either by a central processor or a PLC (Programmable Logic Controller).
It is an object of the present invention to provide a spray booth sludge recovery system which is maintenance free and keeps not only the booth but also sludge system, itself, clean.
Another object of the present invention is to closely control the water quantity in the booth sludge recovery system.
Still another object of the present invention is to closely monitor the water level in the sludge recovery system so that a flotation spent paint recovery system works well.
A further advantage of the present invention is to closely monitor the water level to maintain consistent water crests over a weir.
Yet a further object of the present invention is to maintain consistent flowage over the sludge collection weir.
Yet another further object of the present invention is in providing agitation in the weir box and/or elsewhere in the system to increase centrifuge efficiency and keep the weir box and/or other portions of the system clean.
Still a further object is to provide scavenging early in the sludge recovery system to remove large clumps, particularly before reaching the chemicals treatment section of the booth.
Still yet a further object is to provide a means for a maintenance cycle whereby the booth, tank and/or sludge removal system is cleaned during downtime.